The present invention relates to an apparatus and a method for measuring the curvature and the slope of ground surfaces in two different directions by means of a drivable unit.
Researchers and people responsible for road maintenance need information especially on the crossfall, the curvature and the hilliness of roads to be able to take relevant steps e.g. in respect of public road repairs and maintenance to obtain maximum cost efficiency. Correct road maintenance means optimum bearing strength of the road and a minimum of traffic perils and environmental problems. Such optimum maintenance efficiency requires direct information on the crossfall, the curvature and the hilliness, as well as information which can be indirectly obtained by using these variables for drawing maps so as to make it easier to locate all the variables measured, e.g. road-surface variables. By simultaneous measuring, variables can be linked together, making it possible, for instance, to establish the risks of aquaplaning at the end of a slope, in the presence of ruts and a slight crossfall, possibly also with small texture, increasing such risks.
In road measuring contexts, such information may prove highly profitable, not only for acquiring more knowledge in view of road maintenance, but also for monitoring newly-built surfaces and providing basic data for contracts in connection with the planning and construction of roads.
Since all paved roads in Sweden are now measured regularly, the new variables provided by the present invention can be measured without any substantial additional costs. Thus, the economic benefits of the invention are more appreciable.
U.S. Pat No. 3,797,124 discloses a slope-measuring device which is especially designed for measuring the roadway inclination in the longitudinal and the transverse direction and which has an electric slope-sensitive unit with a slope-sensitive pendulum suspended freely swinging in the slope-measuring direction, i.e. an inclinometer. When the inclinometer is tilted sideways, e.g. owing to the crossfall of the road, the pendulum tends to move in the direction of the crossfall, and the movement is converted by a sensor into an electric signal.
European Patent Application 83100872.7 now European Patent No. 85924 discloses a measuring device which is especially designed for measuring the roadway inclination in the longitudinal and the transverse direction by means of an electric slope-sensitive unit. This unit has a slope-sensitive pendulum suspended freely swinging in the slope-measuring direction and is connected to an indicating unit with a differential transformer whose movable core forms the slope-sensitive pendulum and which is connected to an additional transformer which, by transistors, converts the pendulum movements into proportional electric signals.
Such modern electronic angle sensors or inclinometers measure the angle to the horizontal plane, provided that they are subjected only to the force of gravity. Thus, the angles of inclination can only be correctly measured under fairly static conditions. If mounted in vehicles driven in normal traffic, inclinometers of this type are exposed to forces of acceleration caused by the movements of the vehicle. Thus, this makes a contribution to the output signals by accelerations and decelerations caused by depressing the accelerator or braking, cornering and so forth.
It is known to employ gyro systems which, as output signals give angles to the horizontal plane for determining the horizontal curvature, the vertical curvature and the crossfall. However, gyro-based systems have their deficiencies, such as complicated handling procedures, a great need of attendance and maintenance, sensitivity to external influence and high initial costs, or alternatively poor accuracy.